declare name bandfilter declare version declare author Grame declare l

declare name        "bandfilter";
declare version     "1.0";
declare author      "Grame";
declare license     "BSD";
declare copyright   "(c) GRAME 2006";

import("math.lib");
import("music.lib");

//---------------------second order filter--------------------------
// filter(Q,F,G)
//              Q : quality factor [1..100]
//              F : frequency (Hz)
//              G : gain [0..1]
//------------------------------------------------------------------

filter(Q,F,G)   = TF2(  (1 +  K/Q + K*K)    / D,
                         2 * (K*K - 1)      / D,
                        (1 - K/Q + K*K)     / D,
                         2 * (K*K - 1)      / D,
                        (1 - V*K/Q + K*K)   / D
                     )
        with {
                V = db2linear(G);
                K = tan(PI*F/SR);
                D = 1 + V*K/Q + K*K;
        };



//--------------- Band Filter with user interface ------------------
// bandfilter(F)
//              F : default frequency (Hz)
//
//------------------------------------------------------------------

bandfilter(F)   = filter(   nentry("Q factor",50,0.1,100,0.1),
                            nentry("freq (Hz)", F, 20, 20000, 1),
                            0 - vslider("gain (dB)", 0, -50, 50, 0.1)
                        );



//------------------------- Process --------------------------------

process         = vgroup("Bandfilter", bandfilter(1000));